Electrochemical hydrogen storage properties of Mg–Al–Mn–Ni quaternary alloys

Al was partially substituted by Mn in Mg₃AlNi₂ to improve the discharge capacity and electrochemical kinetic properties of Mg₃AlNi₂ alloy electrode. By means of pretreatment of ultrasonic dispersion, followed by mechanical milling and combustion synthesis, a series of quaternary alloys, namely Mg₃Al_1-xMn_xNi₂ (x = 0, 0.2, 0.4, 0.6, 0.8) were synthesized. X-ray diffraction analysis shows that partial substitution of Mn for Al can cause lattice expansion of Mg₃AlNi₂ and the samples all appear similar multiphase structures. The introduction of Mn enhances obviously the maximum discharge capacity of Mg₃AlNi₂ alloy electrode. The high rate dischargeability of the alloys can also be remarkably enhanced by substitution of Mn for Al. The exchange current density (I₀) and charge transfer resistance (R_ct) of the alloy electrode increase and decrease continuously with increasing the Mn substitution content, respectively, indicating the improvement of electrochemical kinetics properties. Combining with the potentiostatic discharge test, it is concluded that in the Mg–Al–Mn–Ni quaternary alloys, the kinetic properties are mainly controlled by charge transfer reaction on the electrode surface.